In general, a valve is a device wherein a ball type disk rotates in a straight line-shaped flow passage at a right angle or a split angle, thus opening or closing the valve or changing the direction of flow.
Such a valve is easy to use and has a relatively good sealing is performance and allows the flow passage of the valve to open precisely in straight line when the valve is open, so pressure drop is less, and it is advantageous that the opening and closing may be performed with higher reliability even when the valve applies to the fluid wherein the viscosity of impurity such as sludge, etc. is high.
The butterfly valve among the conventional vales is a valve which opens and closes as a disk (a circular plate) rotates about a central line of the circular plate. Since the opening and closing operations are easily performed, the operation is quick, and such a butterfly valve has been widely used for low pressure water as well as high pressure water or vapor, air and gas.
FIG. 1 is a schematic exemplary view illustrating the configuration of a conventional high performance butterfly valve.
As illustrated in FIG. 1, a disk 40 is secured to a rotation shaft 30 disposed at an inner side of a liner 20 secured to a valve body 10, and as a handle 50 rotates, the disk 40 rotates, thus opening or closing a fluid transfer hole (not illustrated) of the valve body 10, so the movement of the fluid can be limited.
As illustrated in FIG. 2A, the liner 20 secured to the butterfly valve may be manufactured by processing the whole a polytetrafluoroethylene(PTFE) rod or as illustrated in FIG. 2B, the liner may be also manufactured in such a is way that an injection mold is manufactured, and molten perfluoroalkoxy(PFA), which is a plastic material, is injected into the injection mold using an injector.
However, the above-described conventional whole processing method and the manufacturing method using the injection mold entail considerable manufacturing time and expensive cost, so there may be a limit in the manufacturing of a large diameter valve.